NO171049B - LAMINATE FOR USE IN PACKAGING, AND WASHING CONTAINER MADE OF SUCH LAMINATE - Google Patents

Abstract

A laminate providing an effective barrier to the migration of essential oils and/or flavourings, such as d-limonene, therethrough is provided comprising, from the outer surface to the inner surface, a paperboard substrate (10'), a web (12') of propylene polymer coated thereon and a web of olefin polymer (14') overlying the propylene polymer web (12'). Preferably the paperboard substrate (10') is also coated on the external surface thereof with a web (16) of heat sealable olefin polymer. Containers constructed from such laminates are especially useful as fruit juice containers which enable significant flavour retention in the fruit juice contained therein over the normal shelf life of the product.

Description

The present invention relates to a laminate for storing essential oils and spices, as well as a container made from such a laminate. More specifically, the invention has a container with laminate that is suitable for use in containers intended for storing liquids containing essential oils and flavourings, such as fruit juice.

For many years, flavor and spice experts have been quite critical of the polyethylene-coated standard cardboard containers that are commonly found on the market, as the essential oils and flavorings included in fruit juice will be able to diffuse through the polyethylene coating itself and be deposited in the cardboard material , whereby the original taste of the fruit juice deteriorates very markedly during the normal storage period.

Although this transport of the essential oils and flavorings will be able to be significantly reduced by using a laminate containing a metal foil in the form of a lining along the inner walls of the container, the expenses in connection with the use of a metal foil will exclude this solution as a viable alternative. Despite the fact that in the past many attempts have been made to replace metal foil with a polymer laminate which, at a relatively low price, will make it possible to preserve the good taste during the entire normal storage period, it has so far largely been unsuccessful in finding a usable Replacement for metal foil.

In the container industry, it has been common practice to use many forms of material which are heat-welded or glued and otherwise converted into a container or carton, using conventional equipment. Such products are usually referred to as "folding boxes", containers or cartons.

As an example, the gable top milk carton and cardboard blank for this can be mentioned, which in US patent 3 120 33 3 are specifically designated as liquid-tight containers. The blanks used in the manufacture of such containers comprise a cardboard substrate which, during extrusion, is coated on both sides with a resin, for example polyethylene, which forms a moisture barrier layer and at the same time enables heat sealing of the carton.

In a typical carton conversion process, after the resin blanks are cut and cut, the resin on the outside of an adhesive flap and the resin on the inside of a cardboard sheet are heated by direct flame action, while the heated cardboard surfaces extend in a controlled position but largely unsupported, i.e. uncompressed, between two heating trays, over the edges of the conveyor belt. During subsequent folding, the cardboard sheets form a flattened tube, as the melted and sticky resin on the heated surfaces is pressed together in a rear-facing clamping zone, to create a liquid-tight side joint. In flattened tube form, the cartons are then transported to consumers, e.g. dairies or juice factories, where they are finally created by further heat welding, to be filled and sealed.

Although these well-known gable top containers have been used extensively throughout the United States for the storage of milk or fruit juice, they suffer from certain shortcomings. One of the disadvantages is due to wetting of the carton's cardboard component.

When piercing the resin and when the coating breaks

or wrinkling along fold lines, other problem areas with a probability of wetting appear. Moisture will also be absorbed, by "wicking effect" or capillary action, through the exposed cardboard material at the edge of the glue flap located in the filled container. Furthermore, certain essential oils can

and/or flavorings that are usually found in fruit juice, e.g. in apple juice, cranberry juice, grapefruit juice, orange juice and the like, penetrate through the moisture barrier layer of polyethylene and into the cardboard, whereby the fruit juice loses its flavor during normal

retention time.

Many attempts have previously been made to eliminate the disadvantages in connection with wetting the cardboard material or the escape of essential oils through the polyethylene moisture barrier layer, with the consequent loss of taste. In an experiment, a lining was used for the inner wall of the container, which consists of two or more layers of polyolefin or other polymer material with an intermediate metal foil. The metal foil present will significantly reduce both the transfer of moisture and the loss of essential oils to the cardboard material. Due to the use of metal foil, the processing is complicated at the same time as the finished product is significantly more expensive.

Other attempts to overcome these problems have resulted in proposals to use homogeneous all-plastic containers that can be produced by blow molding. Due to the fact that such containers are completely designed and that the transport of these includes transport of the air in the containers, the shipping costs will increase considerably in line with the shipping costs for the same amount of containers that can be transported in a flattened state. The containers are also difficult to adapt for cheap, printed decorations.

All-plastic container blanks have also been developed which are cut to size and cut in the same patterns as the previously described, resin-coated cardboard boxes. When these plastic containers are advanced through a typical converter for resin-coated cardboard material, however, extra attention and care must be exercised during the side joining by direct flame exposure of the exposed container surfaces.

Although homogeneous all-plastic blanks will possibly be able to be sealed using known heat welding techniques, e.g. a static system in which the heated zones are supported or clamped in, for example between heating trays, none of these known methods are suitable for commercial, high production speeds. Furthermore, due to the use of other sealing methods, the manufacturer will have to acquire other equipment to achieve effective sealing of the all-plastic container, so that the existing and available equipment will become obsolete. Consequently, such all-plastic containers have not been widely accepted commercially.

The purpose of the present invention is thus to produce containers which are suitable for storing fruit juice, while maintaining the advantages of using cardboard as the base material and at the same time eliminating both the manufacturing and the economic disadvantages of using metal foil.

This purpose is achieved by a laminate and a container as stated in the subsequent claims 1 and 2, respectively.

It has been established that containers made from the laminate according to the invention make it possible to preserve the taste of the fruit juice content to a significant extent, with the consequent significant extension of the possible storage time for the product at the same time as considerable financial savings as a result of the otherwise necessary barrier layers of aluminum foil have been replaced by another material.

Admittedly, US patent 3,553,073 discloses a laminate composed of layers that largely correspond to the layers in the laminate according to the present invention, but this known laminate lacks the adhesive layer of ethylene methacrylate which, among other things, characterizes the laminate in the invention, and is also not the patent indicated some further adhesive layer, as on the contrary one gets the impression that pre-treatment or adhesive should not be used. Furthermore, it is known from GB patent document no. 1080649 to use polyolefins in connection with laminates to protect against grease, oil and moisture, but nothing is indicated that pretreatment or an adhesive is necessary and that such a polyolefin layer should be able to adhere to a adjoining polyethylene layer in the laminate.

It can also be mentioned that the Handbook of Adhesives, second edition, 1976, edited by Irving Skeist, describes a pressure-sensitive adhesive consisting of a copolymer of methacrylic acid and states that EMA resin as a copolymer of ethylene can be used as an adhesive for thermoplastics, while GB patent document 1241223 deals with polyolefins glued together by pressure-sensitive adhesive. However, the laminate according to the present invention is not based on the use of pressure-sensitive adhesives, and its distinctive features will not in any way be obvious to a person skilled in the art who is familiar with the latter literature and patent document. Finally, NO specification 161301 can be mentioned which describes a packaging film composed of polyolefin layers bonded together with an EMA copolymer, but without specifying the new and distinctive features of the laminate according to the present invention.

The invention is described in more detail below with reference to the accompanying drawing, where: Fig. 1 shows a vertical section of an embodiment of the laminate according to the invention.

The described invention is particularly suitable as a cardboard laminate for use in the manufacture, for example, of containers of various types. Of such containers, for example, folding boxes, square or rectangular containers or cartons or simple, cylindrical tubes with a lower closing device and usually also an upper closing device can be mentioned.

It can be mentioned, solely as an example, that the present invention is highly suitable for use with a container type of special design, namely the gable-top container, for storing liquids, which is known, for example, from US patent document 3,120,333.

The laminate according to the present invention, which is shown in fig. 1, comprises a cardboard support layer 10 which preferably consists of high-quality cardboard material, for example 0.254-0.711 mm milk carton material which is coated on one side with propylene polymer 12 in a weight amount of 2.3-13.6 kg/rice. Any propylene polymer is believed to be suitable for use in this connection, for example polypropylene homopolymer, copolymers of propylene and other olefins which are copolymerizable and where the propylene makes up at least approx. 75% by weight of the copolymer, and other modified propylene polymers can be advantageously used. Most preferred is the use of a polypropylene of extrusion coating quality. Typical of such extrusion coating grade polypropylenes are Gulf polypropylene 7914 and 7117 marketed by Gulf Oil Chemical Company, Orange, Texas.

Above the polypropylene layer 12, a heat-sealable olefin polymer 14 is arranged which will form the final inner surface of the manufactured container. The olefin polymer preferably consists of polyethylene and most preferably of a low-density polyethylene. Typical of the preferred low density polyethylenes that may find use as layer 14 is Gulf 4517 polyethylene supplied by Gulf Oil Chemicals Company, Houston, Texas. The olefin polymer layer 14 is applied in an amount by weight of 2.3-13.6 kg/rice. The mutual coating weight ratio between the layers of propylene polymer and olefin polymer should be between 50:50 and 75:20.

The cardboard carrier layer 10 is coated on its other side or outer side with a layer of heat-weldable olefin polymer 16, preferably polyethylene and preferably low-density polyethylene. This outer coating of olefin polymer makes the finished container construction heat-weldable, and also gives the cardboard material a glossy surface which, by suitable but conventional means, can be applied directly to a printed test.

In order to increase the adhesion between the olefin polymer layer 14' and the propylene polymer layer 12, an adhesive layer 18 in the form of a copolymer of ethylene and methacrylic acid (EMA) is arranged between the layers. When using EMA, it has proven particularly beneficial to expose the produced laminate to electron irradiation in a dose of approx. 10 megarad, to achieve cross-linking of the EMA and strengthen the connection between the olefin polymer layer 14' and the propylene polymer barrier layer 12'.

The laminate according to the invention can be easily produced. Thus, the layers of propylene polymer and olefin polymer, respectively, can be extruded together directly onto the cardboard carrier layer. In order, as mentioned above, to favor the adhesion between propylene polymer and olefin polymer, an EMA layer is extruded between the propylene polymer and olefin polymer layers, at the same time that these layers are extruded together on the cardboard carrier layer. A two-stage coating application process is used during which the propylene polymer layer is extruded onto the cardboard carrier layer and the resulting propylene polymer coated cardboard material undergoes any flame treatment, corona discharge or the like, to increase adhesion, after which the propylene polymer barrier layer is covered with an overlying layer of olefin polymer.

The unique barrier effect against the passage of essential oils and flavorings of the laminate according to the invention is clearly evident from the subsequent leveling example.

1.9 liter orange juice containers of the standard type were manufactured and filled with orange juice. The main essential oil in orange juice consists of d-limonene. The filled containers were stored for six weeks, after which the orange juice was analyzed to determine the weight percent loss of d-limonene essential oil and the weight percent loss of vitamin C.

1.9 liter orange juice containers of standard type var

made from a laminate consisting (outside and inside) of 3.5 kg/rice polyethylene, 0.61 millimeter milk carton material and 9.1 kg/rice polyethylene.

Another standard 1.9 liter orange juice container was modified with an aluminum foil inner liner. The outside of the container consisted of 3.5 kg/rice low density polyethylene, 0.61 millimeter milk carton material, 4.5 kg/rice low density polyethylene, 0.009 mm aluminum foil and 9.1 kg/rice low density polyethylene.

A third leveling container was made by modifying the standard 1.0 liter orange juice cardboard container with an inner liner of high density polyethylene. This container consisted externally of 3.5 kg/rice low density polyethylene, 0.62 millimeter cardboard material, 4.5 kg/rice high density polyethylene and 4.5 kg/rice low density polyethylene.

Finally, the laminate according to the invention produced a 1.9 liter orange juice cardboard container of a standard type consisting, outside and inside, of 3.5 kg/rice polyethylene, 0.61 millimeter milk carton material, 4.5 kg/rice polypropylene of extrusion coating quality and 4 .5 kg/rice low density polyethylene.

Table I below indicates the results of quality tests after a six-week storage period.

It is clear that the container which was made from a laminate according to the present invention formed largely the same barrier for the d-limone as the laminate containing aluminum foil. Although it did not form as good a barrier for vitamin C as the container with a lining of aluminum foil, the container of the laminate according to the invention nevertheless formed a better barrier against the loss of vitamin C than hitherto possible without

use of a lining of metal foil.

The effectiveness of the laminate according to the invention as a barrier against the passage of essential oils and flavoring substances enables a significant extension of the storage time for containers made from the laminate, and allows the replacement of a barrier layer of aluminum foil in such containers, with consequent significant cost savings.

Claims (2)

1. Laminate for use in packaging, for creating an effective barrier against the passage of essential oils and/or flavorings, comprising a cardboard layer (10) which is coated on one side with a propylene polymer layer (12) which, on the other hand, is opposite the cardboard layer is coated with an olefin polymer layer (14), characterized in that an adhesive layer (18) of ethylene methacrylate is arranged between the propylene polymer layer (12) and the olefin polymer layer (14), that the layers (12, 18, 14) of propylene polymer, adhesive ethylene methacrylate and olefin polymer respectively is extruded simultaneously on the cardboard layer (10), and that the other side of the cardboard layer (10) is coated with a layer (16) of heat-weldable olefin polymer. 2. Container for liquids containing essential oils and/or flavourings, manufactured from a laminate comprising a cardboard layer (10), coated with a propylene polymer layer (12), which in turn is coated with an olefin polymer layer (14), characterized by that an adhesive layer (18) of ethylene methacrylate is arranged between the propylene polymer layer (12) and the olefin polymer layer (14), that the layers (12, 18, 14) of respectively propylene polymer, adhesive ethylene methacrylate and olefin polymer are extruded simultaneously on the cardboard layer (10, and that the the other side of the cardboard layer (10) is coated with a layer (16) of heat-weldable olefin polymer.